This invention relates generally to the storage of high resolution information by, and with, the use of holography; and, more particularly, to a unique contact printer which is useable in producing a high resolution hologram in which the high resolution information is stored.
High resolution information may be stored by a method which essentially comprises three steps. The first of these steps is exposing a preselected diffraction grating (such as by interferring two plane wavefronts derived from a common coherent source, e.g., a laser, or by using a Roche ruled grating in a doubling self-image process) on the light-sensitive front surface of a suitable photoresist material, such as one deposited to a depth of 3 or 4 micrometers on a stable substrate (e.g., glass, or "Mylar"), thereby forming and preserving the recorded diffracting grating as a latent image which is stored in the solubility of the exposed photoresist surface material of the recording medium. The next step is exposing the same light-sensitive front surface of the photoresist to the high resolution information that is to be stored thereon and therein. This second exposure may be accomplished by an imaging process, wherein an incoherent light source and lens system are used, to transfer the image of the information to be stored (e.g., a pictorial scene, or other pattern, on a transparency) to the same light-sensitive front surface of the previously exposed, but still not developed, photoresist. The last of the steps is developing the photoresist by conventional methods. This developing causes a relief to be formed on the front surface of the photoresist material. This relief records, in the depth of the photoresist material etched away, the information imaged (and now stored) on the front surface of the photoresist.
It is here to be noted, and to be remembered, that the light-sensitive front surface of the photoresist was double-exposed. Therefore, upon development of the photoresist, mixing of the information (from the original diffraction grating exposure, and also from the later transparency image exposure) results in a combined (i.e., a composite second diffraction grating having a frequency determined by the exposures, but with an efficiency that is spatially modulated in accordance with the stored information.
However, if (as is presently the situation in the art) the information is for use in a volume production duplication system that is to be capable of storing, and of rapidly and inexpensively duplicating and displaying 9-inch by 9-inch data frames (or, more importantly, 9-inch continuous web data format), and if the second exposure is accomplished by a lens imaging system (as discussed above), then the imaging lens which is required is one that is capable of preserving 300 line pairs per millimeter over the 9-inch by 9-inch format. This implies a lens system capable of carrying 9.68 .times. 10.sup.4 line pairs across the diagonal. Although a low f/number lens operating in the blue region of the optical spectrum is theoretically capable of imaging the required number of line pairs in a 1:1 imaging system, practical considerations associated with the assembly of such a lens result in the conclusion that the resolving capability of finite conjugate imagery systems limit the information transmission characteristics of the lens to a total of approximately 40,000 line pairs, or a format of approximately 4-inches by 4-inches. Therefore, there is a genuine and current need for a lensless system to eliminate this constraint.
We have invented such a lensless system, which said system is structurally incorporated as a constituent of my unique contact printer. Thereby, we have significantly advanced the state-of-the-art.